What form of "weapons of mass destruction" can terrorists likely acquire and utilize against the US, and what measures can the government put into place in order to stop such an attack?

There are three broad categories of “weapons of mass destruction” (WMD): nuclear, chemical and biological. Especially within the latter two categories, there are numerous types of chemical and biological weapons that could potentially be used by terrorist organizations, and those large numbers make far more difficult the challenge of preparing to defend against each one.

The fear of WMD in the hands of terrorist organizations has preoccupied U.S. national security experts since the end of the Cold War. The attacks by al Qaeda on September 11, 2001, greatly exacerbated those fears, and the government has since placed great emphasis on developing abilities to detect the presence of such weapons, to disable them when found, and to treat the victims before the numbers of deaths associated with their use reach catastrophic levels. Nuclear weapons are generally considered the most catastrophic because of the instantaneous infliction of massive numbers of casualties that result from a nuclear explosion. Fortunately, nuclear weapons, even the smallest tactical nuclear weapons developed by the U.S. and the Soviet Union during the Cold War, are also the most difficult for terrorists to replicate or steal. (The smallest nuclear weapons are small enough to fit into a backpack, and were developed so that soldiers could destroy key mountain passes and other geographic and manmade avenues through which an enemy army could launch an invasion. They were also developed to enable the covert destruction of enemy maritime ports, dams and other wartime targets.) While fully assembled nuclear weapons are difficult to steal and their construction very difficult for terrorists to undertake, the possession of the nuclear or fissile materials that are key components of nuclear weapons is theoretically easier to attain. Once obtained, the fear then becomes of a terrorist attack using a “dirty” bomb: A conventional explosive is used to scatter radioactive debris across a broad area, like in a heavily-populated city.

Chemical and biological weapons attacks are also possible, although each presents significant challenges for terrorists as well as for intended victims. During the Cold War, the Soviet Union was very active in developing new strains of various diseases like Small Pox, Tularemia, Venezuelan Equine Encephalitis, Anthrax, and many others – all in clear violation of the Biological Weapons Convention of 1972. A senior level defector from the Soviet Union’s highly-secret biological weapons program, Ken Alibek, has described a vast effort dedicated at developing, manufacturing and stockpiling these devastating weapons. Should terrorists succeed in obtaining, through theft, bribery, or other means, any of these weapons, tens of thousands, potentially millions, could die. Water supplies and agricultural industries could be contaminated with biological weapons, and just the mass fear that would accompany reports or rumors of such an event would paralyze communities.

Chemical weapons, similarly, can be developed or potentially purchased from a black market. The 1995 Tokyo subway sarin attack carried out by a fringe cult group known as Aum Shinrikyo “only” killed 12 people, but it sickened over one thousand. Had the attack involving the highly lethal nerve agent been better executed, thousands could have easily died. In 2002, a group associated with al Qaeda was caught planning an attack in London involving ricin, a highly toxic derivative of the castor bean that had been used during the Cold War by the Soviet KGB intelligence service in 1978 to assassinate a Bulgarian defector named Georgi Markov coincidentally also living in London. Similarly, the KGB used cyanide gas to assassinate Ukrainian nationalists during the 1950s, employing a young assassin named Bogdan Stashinsky to carry out the murders. Such tactics could be employed by terrorist organizations in the future on a mass scale.

Clearly, if it were so easy to use WMD, al Qaeda would presumably have already done so. It is known that al Qaeda scientists were interested in developing or acquiring chemical and biological weapons – a main reason why the Clinton Administration destroyed a pharmaceutical factory in Sudan in 1998 suspected of being used by Usama bin Laden’s followers to develop chemical and/or biological weapons. The challenge for terrorists, however, is apparently more difficult than previously thought. It should not, however, be taken for granted that terrorists won’t eventually succeed in obtaining chemical or biological weapons, or the materials needed to detonate a “dirty bomb.”

Especially since 9/11, the U.S. Government has invested a great deal of time and money in developing technologies to help detect the presence of chemical, biological and radiological weapons and components. Sensors designed to “sniff” the presence of key ingredients are being researched, and additional efforts have been expended to train “first responders” – police, firefighters, paramedics – in ways to respond to potential attacks employing WMD. The U.S. and many other governments in Europe scrutinize applications by privately-owned companies seeking to export technologies that could be diverted to illicit uses, such as nuclear weapons components that also have benign commercial applications. Such dual-use items present an enormous challenge, as seemingly innocuous items can be used for dangerous purposes. Mix the right two or three otherwise innocent chemicals together, and you have a chemical weapon. Monitoring such activities among organizations that know how to conceal their efforts is an enormous challenge for U.S. and allied intelligence agencies.